A goblet contains $6$ red jelly beans, $9$ green jelly beans, and $6$ blue jelly beans. If a jelly bean is randomly chosen, what is the probability that it is blue?
Explanation: There are $6 + 9 + 6 = 21$ jelly beans in the goblet. There are $6$ blue jelly beans. The probability is $ \frac{6}{21} = \dfrac{2}{7}$.